Friction welding (FW) is a process of joining two components which may be made from the same or different materials. The FW process typically involves pressing one of the two components against the other component with a large amount of force and rapidly moving one of the two components with respect to the other component to generate friction at the interface of the two components. The pressure and movement generate sufficient heat to cause the components to begin to plasticize. Once the two components are plasticized at the contact interface, the relative movement of the two components is terminated and an increased force is applied. As the components cool in this static condition, a weld is formed at the contact interface.
The weld obtained using FW is a solid state bond which is highly repeatable and easily verifiable. For example, the amount of material donated by each component to the formation of the weld, which is referred to as “upset”, is well defined. Therefore, by carefully controlling the energy input into the FW system in the form of friction and forging pressure, the measured upset of a welded assembly provides verification as to the nature of the weld obtained.
As discussed above, relative movement of the two components is a critical facet of FW. Different approaches have been developed to provide the required relative movement. One widely used approach is rotational friction welding (RFW). RFW involves rotation of one component about a weld axis. RFW provides many benefits and is thus a favored welding approach in various industries including aerospace and energy industries.
RFW, however, does have some limitations. For example, in forming a weld, the interface between the two components must be evenly heated to generate a uniform plasticity within each of the components throughout the weld interface. If one area becomes hotter than another area, the material in that hotter area will be softer, resulting in an incongruity in the formed weld. To provide consistent heat generation throughout the component interface, the rotated component is necessarily uniformly shaped about the axis of rotation, i.e., circular. Moreover, since the heat generated is a function of the relative speed between the two materials, more heat will be generated toward the periphery of the rotated component since the relative speed at the periphery is higher than the relative speed at the rotational axis.
In response to the limitations of RFW, linear friction welding (LFW) was developed. In LFW, the relative movement is modified from a rotational movement to a vibratory/oscillatory movement along a welding axis. By controlling the amplitude and the frequency of the linear movement, the heat generated at the component interface can be controlled.
LFW thus allows for welding of a component that exhibits substantially uniform width. LFW, like RFW, is subject to various limitations. One such limitation is that in order to achieve the frequency and amplitude necessary to realize a weld, a LFW device must provide for rapid acceleration from a dead stop. The moving component must then be completely stopped and reaccelerated in a reverse direction. As the size of the vibrated component increases, the momentum that must be controlled becomes problematic. Thus, traditional LFW devices incorporate massive components which are very expensive.
In response to limitations in LFW devices, U.S. Pat. No. 8,070,039, which issued Dec. 6, 2011 disclosed a LFW device with two power shafts. The phasing of the two power shafts in the '039 patent, the entire content of which is herein incorporated by reference, is controlled in order to generate an oscillatory movement of a ram which forces movement between two workpieces which are forced together by a pressing assembly. The '039 patent discloses the use of independent motors whose speed is specifically controlled in order to establish the desired phasing of the shafts.
A LFW system and method which provides consistent welds would be beneficial. A LFW system and method which allows for smaller components within the system would be further beneficial. A LFW system and method which reduce the complexity in motor control associated with the LFW process would be further beneficial.